Winter smog: More common than you think

Many people associate smog with warm, balmy summer days. While true, smog can actually occur more frequently during winter.

"People usually associate air pollution with warmer weather," Christina Daly of Health Canada told TheWeatherNetwork.com. "However there are certain areas in Canada, Montreal for example, where air quality is also affected during the winter months"

In the past, Montreal has seen some of the highest levels of smog in winter. In 2009, the city recorded 21 smog days from November to January alone. And in 2010 there were 17 smog days in the winter compared to seven in the summer.

According to Environment Canada, winter smog is generally a local phenomenon that is exacerbated by cold, calm weather. The agency says fine particles play a significant role in the formation of smog.

While industrial activity and public transport are the main sources of smog in summer, fireplaces and wood-burning stoves are responsible for more than 60 per cent in winter.

"On winter evenings, some residential neighbourhoods may be more polluted because of the high number of wood-burning stoves and fireplaces," adds Daly.

Smog can have a significant impact on one's health, especially for people with asthma and cardiovascular or respiratory disease. Daly says keeping a close watch on smog warnings and air quality forecasts is just as important in summer as it is in winter.

"Canadians enjoy outdoor activities year round and the Air Quality Health Index can help us decide the best times to be active, regardless of the season."